Utilizing Soil Centrifugation for Accurate Estimates of Carbon Dioxide Removal via Enhanced Rock Weathering.

Enhanced rock weathering (ERW) is a promising CO2 removal (CDR) strategy that aims to accelerate the natural process of silicate weathering to increase soil pore water alkalinity and sequester CO2. However, the measurement, reporting, and verification (MRV) of ERW remains challenging due to existing limitations of aqueous-phase sampling methodologies, such as passive and tension lysimeters, which may not fully capture weathering fluxes across varying soil moisture conditions. This study assesses the potential of a centrifugation-based pore water extraction method to improve the accuracy and reliability of ERW measurements. Using a forest ERW trial in Wales, UK, we compared the chemistry of soil pore waters obtained via lysimeters and centrifugation from feedstock-amended and control plots. The centrifugation method detected elevated total alkalinity and Ca concentrations in soil pore waters from feedstock-amended soils, whereas the effect of feedstock amendment was not detectable in pore waters extracted with lysimeters. The high tensions applied during centrifugation likely capture weathering products dissolved in meso- and micropore water, which lysimeters cannot extract. These findings suggest that centrifugation provides a scalable, low-cost approach for ERW monitoring, with implications for improving existing MRV protocols.